Compounds having a quinolonecarboxylic acid skeleton are used as a quinolone type synthetic anti-bacterial agent for curing infectious diseases, but no compound having a carbon-carbon bond between the carbon atom of an isoindoline ring and the carbon atom at the 7-position of a quinolonecarboxylic acid skeleton has been reported at all.
Norfloxacin, Ciprofloxacin, Ofloxacin and the like which have been widely used in clinic as a quinolone type synthetic antibacterial agent are not sufficient in activity against Gram-positive bacteria, in particular, MRSA. Accordingly, there is desired the development of synthetic antibacterial agents which are effective also against these bacteria and have a broad antibacterial spectrum.